Cellular systems in general suffer from co-channel interference. For example, simultaneous transmissions may use the same physical resources and thus generate mutual interference. This co-channel interference reduces the signal quality, which may be measured as signal to interference plus noise ratio (SINR). The reduced signal quality in turn reduces the system capacity.
Future wireless networks, e.g. 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) and 3GPP LTE Advanced, with a more dense deployment of access nodes, e.g. base stations (BSs), or with a higher density of users will most probably remain interference-limited.
There exist proposals to use an approach of cooperative signal communication, e.g. in 3GPP LTE Advanced which refers thereto as cooperative multipoint transmission and reception (COMP). In this approach, receive (Rx) signals are collected from a plurality of BSs for implementing uplink (UL) cooperation, and transmit (Tx) signals are transmitted from a plurality of BSs for implementing downlink (DL) cooperation.
In UL cooperation, several receiving access nodes, e.g., base stations (BSs) or remote radio heads (RRHs), receive a signal from a mobile terminal, also referred to as user equipment (UE), thereby obtaining multiple Rx signals from the terminal. The Rx signals are then communicated between access nodes and jointly processed, e.g. at a central node or at a serving BS.
In DL cooperation, a central node or a serving BS distributes a Tx signal to several transmitting access nodes, e.g. BSs or RRHs. The transmitting access nodes jointly transmit the signal to the terminal.
In both cooperation scenarios, signals may be processed, i.e. by joint reception in UL or joint pre-coding in DL, at a central node or at a serving access node so that co-channel interference is mitigated. Furthermore, the cooperative signal reception or transmission may increase the carrier signal strength.
Cooperation between access nodes allows for increasing the Rx signal quality, in UL cooperation at one of the access nodes and in DL cooperation at the terminal, and capacity of an access link between the terminal and the access nodes.
Soft handover techniques considered in 3GPP for UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access (UTRA) can be considered as a type of UL cooperation between access nodes. In these soft handover techniques, the signal transmitted by the terminal is received in multiple cells, also referred to as active set, thereby obtaining multiple Rx signals. The multiple Rx signals are then combined in a central node, referred to as Radio Network Controller (RNC), according to selection combining.
Further, several adaptation techniques are known, which may be used to address issues like quickly varying channel conditions and interference level. For example, it is known to adapt a Modulation and Coding Scheme (MCS), to adapt the Tx power, or to change the resource allocation in time and frequency domain. Such adaptation techniques may be implemented, e.g. in a serving BS. However, these known adaptation techniques do not take into account cooperative signal communication scenarios.
For example, the parameters for an UL transmission like MCS, Tx power or resource allocation may be selected based on an Rx signal quality value of a communication link between a terminal and its serving BS. Cooperative signal communication increases the UL Rx signal quality by leveraging the multiple channels from the terminal to a plurality of BSs. The improved cooperative Rx signal quality will thus not be taken into account when adapting the parameters for UL transmission. Further, the type of cooperative signal communication may vary frequently. As a result, the cooperative Rx signal quality varies frequently depending on the type of cooperative signal communication. By simply considering the last signal quality measurement or an average over the last measurements, it is therefore not possible to quantify the future cooperative Rx signal quality and to use it for adaptation. Consequently, the potential of cooperative signal communication will not be fully exploited.
Accordingly, there is a need for techniques that overcome the aforementioned problems and allow for efficiently utilizing cooperative signal communication in a communication network.